In various orthopedic surgical procedures, it is necessary to secure portions of a spinal column in a relatively fixed relationship. This need is often the result of disease, damage or congenital deformation. For example, when one or more intervertebral disks of the spine degenerate due to trauma or disease, the spinal cord or emergent nerve can become compressed. This condition results in chronic and sometimes debilitating neck, back, or peripheral nerve pain. It has become increasingly recognized that fusion between two adjacent vertebral bodies in the space occupied by the implant is desirable for biomechanical, neurophysiological and anatomical reasons. This “interbody fusion” is biomechanically advantageous because the area to be fused is subjected to compressive loads rather than tensile forces as in the case for posterior element fusions. Biologically, it also has favorable characteristics with a favorable blood supply allowing for graft incorporation and, ultimately, healing. It also offers the best way to restore or maintain the opening of the neuroforamina and to restore or maintain lumbar lordosis. Quite often, spinal deformity correction cannot adequately be performed without interbody surgery. The goals of interbody fusion are (1) to maintain sagittal and frontal plane alignment, (2) to maintain or restore intervertebral space dimension, and (3) to achieve a solid fusion. A number of surgical techniques and graft materials have been utilized to attain a safe and successful pain relieving fusion.
Implants are used to form supports for interbody fusions, whereby, after at least a partial removal of an intervertebral disc and preparation of the roof plates of the vertebrae, the implant that is to be inserted between adjacent vertebrae is introduced into the intervertebral disc space, and it is ensured that the normal gap between adjacent vertebral bodies is reestablished. By forming the cover surfaces facing the adjacent vertebrae with a porous surface or providing them with a profiled structure, the allograft arrangement will become firmly anchored after the implant has been inserted due to growth of the bones of the adjacent vertebrae onto the cover surfaces of the implant. In addition, or as an alternative, at least one break-through or recess in the cover surface of such an implant may be filled with a bone graft substitute or biological bone material before being inserted so that the bone mass accommodated in the implant will be urged to knit with the material of the immediately adjacent vertebrae after the implant has been inserted. A successful fusion stabilizes the spine, reduces pressure on the spinal cord and nerve roots, and reduces or eliminates back pain.
Implants having substantially cylindrical contours are known, for which reference may be made to EP-A 0 369 603 or DE-C 36 37 314 for example. Such types of cylindrical or tube-shaped implants may be additionally provided with a thread-like outer contour in order to enable them to be screwed between the vertebrae by means of a self-threading action. The particular disadvantage of tube-shaped implants of this type, whereby two implants must be used between each two adjacent vertebrae in normal circumstances, is that the implants do not have a defined substantially flat support area on the vertebrate thus giving rise to the fear that difficulties will possibly be encountered in regard to the growth of the incorporated bony material. This can result in implant subsidence and failure. Biomechanically, these threaded devices can cause damage to the implants which compromise the stability of the construct.
Implants have been made out of various materials from bone grafts such as bovine zenograft and allograft tibia, fibula, femur, iliac crest and autograft iliac crest. Threaded cylindrical “cages” made from either titanium or fresh frozen allograft femoral diaphysis have been used as implants. The stability provided by the threaded design allowed these implants to be used as a “stand alone” device not requiring further stabilization. However, there have been increasing reports of non-union when initially fusion was thought to have occurred and subsidence with sinking of the implants into the vertebral body. These cages require tapping in order to be inserted in the spinal column. Tapping causes destruction of the supportive end plates of the vertebrae allowing subsidence or “sinking in” of the implant into the body of the vertebrae. This causes a loss of height of the spinal column with a narrowing of the foramina and a potential compression of the existing nerve root. There is also a flattening of the lumbar lordosis resulting in lower back pain. Therefore, there is a need for an implant that is easy to insert while preserving the endplates for support of the construct.
LifeNet, a developer of allografts and a tissue bank organization, produces an ALIF implant in its Vertigraft® line of bone wedges and shafts for anterior spinal column support. It has a textured surface for increased stability and resistance to graft migration. However, there are also grooves cut in the top and the bottom of the implant so that an insertion instrument can grip the implant. The presence of these grooves reduces the contact area that the implant can have with the adjacent vertebrae. This in turn reduces the compressive strength of the implant. Therefore, there is a need for an implant with an improved contact area while maintaining a way to grip the implant for insertion in the spine.
One surgical tool that is used in the insertion of implants is a pliers-action implant holder. This allows for impaction of the implant, but poor control of rotation, angulations, and does not allow for fine adjustments while the implant is being seated. Insertion using a poor grasping tool typically allows rotation or lateral displacement of the graft before the surgeon has a chance to make final placement and secure it. Another feature lacking in surgical instruments is the ability to remove the instruments in a way which will not encourage side loosening. When an inserted instrument becomes jammed, lateral movement or force will tend to damage the surrounding areas. The surgeon's lack of control over exit angle as well as entry angle is a problem in performing this type of procedure. This is especially complicated by the fact that major blood vessels lie to either side of the operative area. Therefore, there is a need for an implant insertion device that can be removed from the implant with ease and without damage to the implant and surrounding tissues.
Proper surgical tools should lend themselves for automatic adaptation for patients of different size and of different complications. Therefore, there is a need for an implant insertion device that can accommodate various sizes and conditions of patients.
Implants are typically designed to be inserted from an anterior, posterior, or lateral approach. However, such implants are often designed for insertion only from one of the particular approaches of the spine. This is particularly true where implants are intended to maintain non-parallel angulation between the adjacent vertebrae. Therefore, multiple implants each designed for insertion from one of the various approaches to the spine must be maintained in inventory to accommodate the various surgical demands of each procedure. Maintaining multiple implant designs may create inventory problems for both manufacturers and their customers. Moreover, the complications of creating multiple implants to accomplish the same desired spacing is compounded when implants are made of a scarce resource, such as allograft bone. Therefore, there is a need for a spinal implant capable of being inserted in the body from multiple approaches so that the inventory of implants needed can be reduced and so that bone resources can be optimized. An inserter device designed for this specialized implant is also needed.
It is the objective of the present invention to provide an implant insertion device that can accommodate various sizes of bone implants. It is also an objective to provide an implant insertion device that is capable of inserting a bone implant with ease from both the anterior and oblique directions.